I found this 8 sided coin, it is reeded on the edges; I don’t know what kind of metal it is. Dealers have looked at it and don't know where it's from or anything about it but all say it's definitely a coin; I can see a couple of numbers in the date, I think they are 17 but can’t be positive. The man has a moustache but it doesn’t show in the picture. The back doesn't appear to have any writing however the coin is very corroded so writing could be there. Anyone have any ideas? I'm afraid to clean it in case it's valuable.